The present invention relates to a method for stamping an arm for car suspensions, according to the preamble of claim 1.

In the automobile sector, a prior art arm for car suspensions is manufactured by means of a method comprising the following steps:

• detaching two shaped blanks from a substantially flat plate;
• bending each blank so as to define a relative concave central portion limited by a relative peripheral edge;
• bending a first portion of the peripheral edge of each blank around a first containment matrix;
• drilling a second and a third portion of the peripheral edge of each blank in order to carry out a first and, respectively, a second coupling hole;
• bending a fourth portion of the peripheral edge of each blank around a second containment matrix and in a reference plane placed according to an angle of substantially 90° with respect to a containment plane of said blank; and
• welding the two blanks together along the fourth portion in order to obtain the arm and so that the relative first portions define a seat for coupling with a first bush, the relative first holes define a seat for coupling with a second bush, and the relative third holes define a seat for coupling with a joint.

The known method of the type described above has some drawbacks mainly owing to the fact that the arm is defined by two blanks, and is thus relatively heavy and expensive, it involves the use of said containment matrices and the two blanks must be welded, which is a complex and expensive process.

Document JP-2004042079-A relates to a method for manufacturing suspension parts according to the preamble of claim 1. After forming the base stocks for the suspension parts having common cross-sectional shape, the amount of bending for making the base stocks into a shape in accordance with the kinds of cars is selected wand changed. An approximate plane is formed in the intermediate part situated between end parts by bending the base stock having the end parts situated in the longitudinal direction respectively in the vicinity of the supporting points of the end parts.

It is an object of the present invention to provide a method for stamping an arm for car suspensions that overcomes the drawbacks described above and is simple and inexpensive to implement.

According to the present invention there is provided a method for stamping an arm for car suspensions as set forth in claim 1. Preferred embodiments of the invention are defined in the dependent claims.

The present invention will now be described with reference to the accompanying drawings, illustrating an embodiment thereof, in which:

• figure 1 is a first perspective view of a preferred embodiment of an arm for car suspensions which can be manufactured by the method according to the present invention;
• figure 2 is a second perspective view of the arm of figure 1;
• figure 3 is a schematic diagram of a sequence of steps in order to produce the arm of figures 1 and 2;
• figure 4 is a cross-section along the line IV-IV of figure 3g;
• figure 5 is a cross-section along the line V-V of figure 3g;
• figure 6 is a cross-section along the line VI-VI of figure 3h; and
• figure 7 is a cross-section along the line VII-VII of figure 3h.

With reference to figures 1 and 2, designated as a whole by number 1 is an arm for car suspensions, which is formed in one piece, has an arched shape, and is stamped in a press (not illustrated) starting from a flat plate 2 (figure 3a), which is substantially rectangular in shape, and is made, in this case, of 3 millimetre-thick hot-rolled UHSS Multiphase steel manufactured and sold by ArcelorMittal under product code number M800HY.

As illustrated in figures 3b and 3c, two successive blanking operations are performed to detach two blanks 3 from the plate 2, each one of which is limited, in its initial shape, by two largest sides 3a and 3b which are substantially flat and parallel to each other, and is stamped to define a relative arm 1.

In a third step, each blank 3 is drawn starting from its side 3a, with a first given bending radius, and in correspondence with a central portion 4 thereof limited externally by a peripheral edge 5 extending around said portion 4, an end portion 6 of the edge 5, and an intermediate portion 7 of said edge 5 (figure 3d).

According to that illustrated in figure 3e, in a fourth step, the portions 4, 6 and 7 of the edge 5 are drawn again with a second bending radius smaller than the first bending radius; the portion 4 is drilled to carry out a plurality of functional holes 8 (in this case four holes 8); and the edge 5 is drilled in correspondence with an end portion thereof 9 opposite to the portion 6 to carry out a hole 10 suitable for coupling, in use, with a first bush (not illustrated).

After completing the process of drawing the portions 4, 6, and 7 and drilling the portion 9, the edge 5 comprises a portion 11 extending between the portion 7 and the hole 10, a portion 12 extending between the portions 6 and 7, and a portion 13 extending between the portion 6 and the hole 10 on the opposite side of the portions 11 and 12 with respect to the portion 4 (figure 3e).

With reference to figures 2 and 3f, in a fifth step, the edge of the hole 10 and of one of the holes 8 (hereinafter designated by 8a) is taken off, i.e. these are provided with respective annular collars 14, 15 which protrude from the side 3b; and, in a sixth step, the portions 11, 12, 13 of the edge 5 are bent into relative first bent configurations, in which the portions 11, 12, and 13 are placed according to a first bending angle of substantially 90° with respect to a reference plane P1 (figure 4) parallel to the sides 3a, 3b.

According to that illustrated in figures 2, 3g, 4, and 5, in a seventh step, a first part 11a of the portion 11 and the portion 13 are bent without a containment matrix starting from the relative first bent shapes, below the blank 3, and into relative second bent shapes, in which the part 11a and the portion 13 are placed with a second bending angle different from 0° with respect to relative reference planes P2, P3 which are substantially orthogonal to the plane P1.

With reference to figures 2, 3h, 6, and 7, in an eighth step, the part 11a and the portion 13 are bent again without a containment matrix starting from the relative second bent shapes, below the blank 3, and into relative third bent shapes, in which the part 11a and the portion 13 are placed according to a third bending angle different from 0° and greater than the second bending angle with respect to the relative planes P2, P3.

With regard to the above description, it should be noted that the portion 12 and a second part 11b of the portion 11 adjacent to the part 11a define, in the relative first bent shapes, a seat 16 (figures 1 and 2), in the form of an arc of a circle, and suitable for coupling, in use, with a second bush (not illustrated).

With reference to figures 1, 2, and 3i, in a ninth step, the portion 6 is bent in a reference plane P4 placed according to an angle different from 0° with respect to the plane P1; and the portion 7 is drilled in order to carry out a hole 17 defining, in use, a reference hole for controlling the arm 1 mounting interaxes.

In a tenth step, the blank 3 is placed with the plane P4 substantially horizontal; and the portion 6 is drilled to carry out a hole 18 suitable for coupling, in use, with a joint (not illustrated).

In an eleventh step, the edge of the hole 18 is taken off, i.e. it is provided with an annular collar 19 which protrudes from the side 3b.

In a twelfth step, the hole 18 and the collar 19 are gauged to achieve the tolerance required for coupling with said joint (not illustrated).

Finally, in a thirteenth step, the seat 16 is machined to remove the chippings in order to obtain the shape and tolerance required for coupling with said second bush (not illustrated).

Using the method described above it is thus possible to obtain a monocoque arm 1, which is box-shaped and requires no additional welding operations after the stamping process.